1. Field of the Invention (Technical Field)
The present invention relates generally to the field of ramps for facilitating disabled individuals ascent to and descent from a structure, particularly, the present invention relates to the field of retractable ramps used in motorized vehicles for efficient ingress and egress by wheelchair or scooter occupants.
2. Background Art
Vehicles adapted for mobility-challenged individuals are necessary to provide such individuals the ability to travel in a manner similar to ambulatory passengers. Historically, these vehicles consisted of full-sized vans having an electrical or hydraulic powered wheelchair lift installed on the vehicle to assist wheelchair occupants into and out of the van. These lifts consisted of a horizontal platform that translates vertically to allow the wheelchair or scooter occupant easy access from ground level to the interior of the vehicle for transport.
Recent mobility vehicles are often smaller vans, or “minivans”, having a lowered floor. In these minivans, a section of the floor extending from the firewall to immediately in front of the rear wheel-well is modified such that it is lowered by a predetermined distance from the floor position of the manufacturer. These types of mobility vehicles provide the additional headroom required for a wheelchair occupant to access the interior of the vehicle while remaining seated in the wheelchair.
Some form of ramp allows the wheelchair occupant to be transported from the ground external to the vehicle to the floor within the modified vehicle. The ramp is typically stored in a vertical position in the sliding door entrance that is common to minivans and in the plane of the minivan sidewall. To access the ramp, the ramp is rotated outwardly about a pivot consisting of the lower end of the ramp located approximately at the floor of the van, until the opposite end of the ramp comes into contact with the ground. Examples of this type of ramp mechanism are described in U.S. Pat. No. 4,966,516 to Vartanian entitled, “Vehicle Access Ramp Having Alternative Pivots For Stowing,” and U.S. Pat. No. 5,391,041 to Stanbury et al. entitled, “Hydraulically Operated Bus Ramp Mechanism.”
While these types of ramps are generally reliable in function and provide the necessary access to the mobility vehicle, they block the vehicle entrance when stowed. These ramps also occupy valuable space in the interior of the vehicle and are not aesthetically pleasing.
Attempts have been made to address these issues, such as by positioning the ramp horizontally below the floor of the vehicle and configuring the ramp such that it slides horizontally outward from the stowed position. Once the ramp is fully extended from the stowed position, the far end is lowered to come into contact with the ground. However, this type of ramp also suffers from disadvantages. When the floor of a minivan is lowered, the ground clearance of the vehicle is decreased. Therefore, when installing any type of horizontally mounted ramp, a low profile must be retained to optimize the ground clearance of the vehicle.
Attempts to address the issue of the low profile required with horizontally mounted ramps have met with limited success. One example is described in U.S. Pat. No. 5,636,399 to Tremblay et al., entitled “Movable Ramp Assembly.” The Tremblay patent utilizes a chain drive and side rails having a profile along which cams are driven to move the ramp platform. Wheels or bearings roll along the upper surface of the lip of the ramp platform and allow a flap to come down into position due to a chamfer in the lip of the ramp. This design is inferior in that it does not provide sufficient strength in the center of the ramp flap to allow an ambulatory person to step on the flap in the center of the flap when the ramp is in its stowed position. Further, the cam, or guide wheel profile used to move the ramp requires additional vertical space that reduces the ground clearance beneath the vehicle.
U.S. Pat. No. 5,393,192 to Hall et al. entitled, “Underfloor Extendible Ramp For Vehicles” uses two, toothed drive belts to power a ramp that can be extended from beneath a vehicle floor. The belts are driven from an auxiliary drive shaft that is in turn driven by another drive belt from the motor. One of the limitations of this ramp is that it requires the use of two separate motors; one to drive the ramp mechanism back and forth and a second to rotate the ramp up to floor level.
Another important consideration in slide-out ramp mechanisms is the inclusion of a ramp platform extension, or lip, along the side of sufficient height to prevent a wheelchair occupant from rolling off the ramp while traversing it. To provide adequate ground clearance the height of such a lip is constrained by the amount of storage space available for stowing the ramp when not in use. One example of a patent that includes a side lip on a ramp is U.S. Pat. No. 6,264,416 to Eaton, Jr., entitled “Compact, Slide-Out Ramp for a Minivan.” The Eaton patent describes a drive mechanism mounted below the ramp platform. However, the space occupied by the drive mechanism has the undesirable result of requiring a diminutive ramp side lip in order to maintain a height profile marginally sufficient for ground clearance.
One deficiency of many prior art ramp mechanisms is the lack of a manual release to be used when power is lost to the ramp. A mobility-challenged individual cannot exit a vehicle in an emergency as quickly and easily as an ambulatory occupant making manual control of the ramp crucial. Prior art ramps do not allow quick and easy manual deployment. Most require the use of tools, or the actuation of a lever that can only be accessed from the outside of the vehicle, resulting in arduous and impractical deployment. Such a ramp is described in U.S. Pat. No. 5,636,399 Tremblay et al., supra. The user generally has to remove an access plate covering the drive mechanism and insert a tool, such as a lug wrench onto the end of the drive mechanism, which is usually some type of acme screw. The user then must manually turn the wrench multiple times, typically for several minutes, to deploy the ramp. This is extremely difficult for a person in a wheelchair, particularly when the drive mechanism is mounted below floor level.
Further, if the ramp drive mechanism cannot be released from the motor, the wheelchair occupant must back-drive the system against the resistance of the motor for manual deployment. This type of design is described in U.S. Pat. No. 5,676,515 to Haustein, entitled, “Low Floor Vehicle Ramp.” Another difficulty with prior art ramps is the inability of the ramp to be deployed onto a curb. Many prior art ramps tend to drop down at the far end as they come to the end of their travel upon horizontal deployment from the force of gravity and lack of support at the far end. This often results in the ramp abutting the curb at a point lower than the top surface of the curb such that the ramp is not fully deployed and is unusable.
Still another difficulty with prior art ramps is the manner in which the ramp is transitioned to the vehicle floor. Many ramps rely upon a type of tilting mechanism such as in U.S. Pat. No. 6,238,168 to Cohn et al. entitled, “Ramp Assembly with Locking Mechanisms,” or upon a type of transition flap, a relatively horizontal planar component extending between the near end of the ramp and the floor of the vehicle. Prior designs often provide substandard strength and stability for stepping onto the flap when the ramp is stowed.
Yet another problem with prior art ramps is the method by which the ramp translates back and forth from the stowed to the deployed position. Many ramps use some form of radial ball bearing for translation such as in U.S. Pat. No. 6,264,416, supra, and U.S. Pat. No. 5,380,144 to Smith et al. entitled, “Deployable Vehicle Access Ramp.” The Smith patent uses roller ball bearings and a track mechanism to move back and forth. Still other designs use a low friction bearing material having two flat components that slide against one another, as described in U.S. Pat. No. 6,238,168, supra.